1. Field of the Invention
The present invention relates to a wet processing system for applying a process solution, such as a resist solution or a developer, by a process solution pouring nozzle to a substrate, such as a semiconductor wafer or a glass substrate for a liquid crystal display (LCD substrate), a wet processing method, and a storage medium storing a program specifying the wet processing method.
2. Description of the Related Art
A resist pattern forming process for forming a resist pattern on a substrate is one of the processes for fabricating a semiconductor device or a LCD substrate. The resist pattern forming process includes a series of steps of forming a resist film on a substrate, such as a semiconductor wafer (hereinafter, referred to simply as “wafer”), exposing the resist film through a photomask, and developing the exposed resist film to form a resist pattern. The series of steps is carried out by a coating and developing system.
The coating and developing system includes wet processing units including coating units for applying a resist solution to a wafer, and developing units for applying a developer to the wafer processed by an exposure process. The coating and developing system is provided with plural coating units and developing units to process wafers at a high throughput.
The coating unit for applying, for example, a resist solution, namely, a process solution, to a wafer has a spin chuck, namely, a substrate holding device, and a cup surrounding the spin chuck. A resist solution is poured onto a substantially central part of a wafer held by the spin chuck. The spin chuck is rotated for entirely coating the surface of the wafer with the resist solution by spin-coating and for drying the wafer by spin drying. The coating unit also carries out a side rinsing process.
The resist solution supplied from a resist solution supply unit is poured through a nozzle (process solution pouring nozzle) onto a wafer. In most cases, the nozzle is held at a home position apart from a wafer carrying passage while the nozzle is not in use to avoid obstructing a wafer carrying operation, and the nozzle is moved to a pouring position corresponding to the center of a wafer held by the spin chuck only when the resist solution needs to be poured onto the wafer.
The nozzle excluding its tip part needs to be filled up with the resist solution to start pouring the resist solution immediately after the nozzle has been moved to the pouring position above the wafer. Sometimes, the resist solution drips from the nozzle onto parts of the wafer other than a desired part while the nozzle is being moved to the pouring position when the nozzle is filled up with the resist solution. Consequently, a peripheral part, for instance, of the wafer is wetted with the resist solution. If the wafer is wetted with the resist solution for spin coating by pouring the resist solution through the nozzle positioned at the pouring position onto the wafer so wetted abnormally with the resist solution, a resist film of irregular thickness is formed to cause unsatisfactory exposure. If the spin chuck is wetted with the resist solution, the attraction of the spin chuck is reduced in some cases.
A suck-back valve provided with a suction chamber is placed in a resist solution supply line for carrying the resist solution to the nozzle to prevent the resist solution from dripping when the resist solution does not need to be poured. The vacuum chamber of the suck-back valve is expanded to create a vacuum to retract the end surface of the resist solution in the nozzle to prevent the resist solution from accidentally dripping from the nozzle. In some cases, the retracted end surface of the resist solution is forced to advance by the generation of bubbles by gases dissolved in the resist solution or the expansion of bubbles and the resist solution due to changes in the temperature of the cleanroom. Thus it has been difficult to prevent perfectly the drip of the resist solution onto positions other than a desired position
Recent request for flexible manufacturing of many types of products in small quantities requires selectively using different kinds of resist solutions. It has been a usual method of changing the resist solutions to replace the nozzle held by a nozzle carrying arm for carrying the nozzle with another one. The inventors of the present invention developed a nozzle carrying arm fixedly holding plural nozzles to simplify a nozzle changing operation and to omit a nozzle changing mechanism. When the nozzle carrying arm holding, for example, ten nozzle is moved, the probability of dripping the resist solution is ten times the probability when a single nozzle is held by the nozzle carrying arm, and hence the importance of the drip preventing measures for preventing the drip of the resist solution increases still further.
Efforts have been made to use parts common to the same type of plural wet processing devices included in a coating and developing system to reduce the kinds of parts and to reduce weight. An example of one of such efforts is making studies to develop a coating unit including plural sets each of a spin chuck and a cup (hereinafter referred to as “wet processing devices”) arranged in a line in one box, and one common nozzle arm holding one common nozzle and moving the common nozzle in the wet processing devices by a common nozzle carrying arm to pour a resist solution onto wafers held on the spin chucks. In this coating unit, the common nozzle needs to travel a long distance for a long time. Therefore, it is highly possible that the resist solution drips during the movement of the common nozzle. When a coating unit of this type is provided with a nozzle arm holding plural nozzles, the problem of dripping the resist solution is far more serious than a coating unit of a conventional type.
A monitoring technique using a camera for monitoring the condition of an end part of a nozzle is mentioned in JP-A No. H11-176734, Paragraphs 0017 to 0020 and JP-A 2003-136015, Paragraphs 0090 to 0102, FIG. 14. This monitoring technique is employed in the present invention. Image information about the end part of the nozzle is obtained by the camera while the resist solution is being poured onto a wafer or immediately before and immediately after pouring the resist solution. The image information is analyzed, and the output of a pump included in a resist solution supply unit and the quantity of operation of a suck-back valve are adjusted on the basis of results of analysis of the image information to supply the resist solution constantly or to supply the resist solution uniformly when the nozzles are changed.
Since the camera is installed so as to monitor the nozzle positioned above a substantially central part of the wafer, the camera is unable to monitor the condition of the end part of the nozzle while the nozzle is being carried. Nothing is mentioned in those cited references about techniques for dealing with the foregoing troubles.